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Re: New threaded rod driven arm - 14 years ago
I have finally come up with a solution for an easy reliable coupler you can make out of plastic. The attached STL file is a 3/32 to 1/4 coupler. It is 1/2" long, and 3/4" diameter. It uses 6 #4 nuts that are forced fit into the slots around the hole. This is so that the set screw does not strip out the plastic. 6 #4 X 3/8" set screws go through these nuts and hold the shaft in place. They can beby galaxyman7 - Polar Machines, SCARA, Robot Arms
Re: New threaded rod driven arm - 14 years ago
Have you guys seen the TI Launch Pad? I can't believe how cheap it is. I am sure this is going to be what everyone uses now. I still have my Parallax board, so I will use that for the robot arm, but in the future the Launch Pad is my first choice. Anyways, I have tested the x axis a lot, and I am pretty sure that the end supports have holes that are closer or further away from eachother than thby galaxyman7 - Polar Machines, SCARA, Robot Arms
Re: New threaded rod driven arm - 14 years ago
I have not tried that yet, and that is probably a good idea. I was thinking of using a piece of 1/8" ID, 1/4" OD tubing to cover the 1/8 motor shaft. Then using a 1/4 ID, 3/8 OD tubing to connect to the threaded rod. Do you know where to get very small clamps? I have looked but only found ones for larger hoses. And by the way, I did get the plastic coupler to work, but I have a feeling the setby galaxyman7 - Polar Machines, SCARA, Robot Arms
Re: New threaded rod driven arm - 14 years ago
Unfortunately my Cnc is home made, made out of mdf. When milling aluminum it is horribly inaccurate and aluminum sticks all over the bit. I could try coolant but that still does not affect the accuracy. One problem is holding the aluminum bar when drilling into it. It almost always catches on the bit and gets stuck, spinning around. I do not have an edge finder, and so it is hard to find the exacby galaxyman7 - Polar Machines, SCARA, Robot Arms
Re: New threaded rod driven arm - 14 years ago
Unfortunately I do not have a lathe, just a drill press and a home made cnc. I have some aluminum bar stock, but making a coupler with a drill press has proved to be impossible. The alignment is always off, and the drill bit constantly gets stuck in the aluminum. I was wondering if there would be an easier method using HDPE plastic, which I happen to have tons of. Preferably something I can millby galaxyman7 - Polar Machines, SCARA, Robot Arms
Re: New threaded rod driven arm - 14 years ago
Ok I have been working on stuff, and I just got a bunch of motors out of a printer. I got a big one for the x axis, and a couple small ones for the arm. (similar motor pics attached) The problem is connecting the motors to the threaded rod. I have tried making couplings on my CNC out of plastic, but the set screws just strip the plastic. I have also tried clamping two plastic pieces around a shafby galaxyman7 - Polar Machines, SCARA, Robot Arms
Re: New threaded rod driven arm - 14 years ago
Ok, the teflon lined bushings work great. I just made a few plastic clamping rings with holes around the edge, and then forced each slide into the holes. Then I used zip ties to hold the clamping rings tight. I bolted the clamping rings to the frame, and voila, you have a very low friction slide. It is hard to explain how it works so I uploaded some pictures along with sketches. It is very smootby galaxyman7 - Polar Machines, SCARA, Robot Arms
Re: New threaded rod driven arm - 14 years ago
I like the counter-balance idea. I might even put a weight in addition to the motor. As for the twisting of the arm, that is why I have threaded studs between the two sides of the arm. These studs have nuts between the two sides as well as on the outside. When you tighten them, it fixes the distance and makes sure the two sides stay parallel, preventing twisting. I might even add washers to makeby galaxyman7 - Polar Machines, SCARA, Robot Arms
Re: New threaded rod driven arm - 14 years ago
That sounds cool, but unfortunately I do not have to tools to create something like that. Once this design works, it can print something more complicated like the conveyor belt. Until then I am sticking with what I know will work.by galaxyman7 - Polar Machines, SCARA, Robot Arms
Re: New threaded rod driven arm - 14 years ago
That is a cool idea, except that the parts must stick to the bed when they are created. If there was some way to make it so that the parts did not stick but still came out well, then that would be awesome.by galaxyman7 - Polar Machines, SCARA, Robot Arms
Re: New threaded rod driven arm - 14 years ago
Ok, I am finally ready to work on this thing. I made the arm and changed the x axis to threaded rod. The whole arm slides on two rails. The rails can be however long you want, allowing for a huge print area. The problem is friction with the rails on the plywood. The plywood alone on the rails is not slippery enough even with grease. Therefore I have bought a couple of very cheap teflon lined bearby galaxyman7 - Polar Machines, SCARA, Robot Arms
Re: New threaded rod driven arm - 15 years ago
School gets out in 2 weeks. Then I will definitely get going on this project. I have already built one arm piece and threaded rod assembly, but I can't find my camera, so I won't be able to upload pics until I find it.by galaxyman7 - Polar Machines, SCARA, Robot Arms
Re: Incredible polystyrene 5DOF robotic arm - 15 years ago
These robots are great for pick and place assembly, but I really don't think it is accurate enough to print its own parts.by galaxyman7 - Polar Machines, SCARA, Robot Arms
Re: New threaded rod driven arm - 15 years ago
Sorry I haven't done much lately. I am really busy with school and work. I will try to get some more done soon.by galaxyman7 - Polar Machines, SCARA, Robot Arms
Re: New threaded rod driven arm - 15 years ago
For the motor control, I will be using an SX chip from parallax , plus 4 of these Hbridge driver chips. 4 of these photo interrupters And 4 acrylic disks with contact paper with printed pinstripes on them. (100 per rev) I am not sure if the contact paper will be transparent enough, but it is worth a shot. The SX will interface with the parallel port, taking step and direction signals and movinby galaxyman7 - Polar Machines, SCARA, Robot Arms
Re: New threaded rod driven arm - 15 years ago
The nut and motor holders are made from HDPE on my cnc milling machine. The acrylic sides are also made on the cnc. However, polypropylene is much cheaper and I will probably switch to that. Right now I am trying to come up with a way to calculate the sag of the arm depending on the angles of the joints. The program can then compensate. I am also looking into how to calculate the oscillation ofby galaxyman7 - Polar Machines, SCARA, Robot Arms
Re: New threaded rod driven arm - 15 years ago
Here is a picture of the motor connected to the threaded rod, which is threaded through a nut with a holder around it. Both the motor and nut have bolts coming out from each side. These are to let them pivot.by galaxyman7 - Polar Machines, SCARA, Robot Arms
Re: Robotic arm printer - 15 years ago
It isn't going to use any servos, just the hobby motors from here>> They cost 4.22 each. For the encoder, I will just use paper with black stripes printed onto it, an LED and a phototransistor. So for each motor and encoder, it will be around $5. As for the angular momentum, that is also a reason why I want to use threaded rod, since it cannot be backdriven. I know there will be some oscby galaxyman7 - Polar Machines, SCARA, Robot Arms
Re: Robotic arm printer - 15 years ago
I am still using the geared hobby motors, but the encoder wheel will only need 100 steps around the wheel,giving it .005" accuracy (20 turns per inch) . The motors weigh barely anything (maybe 3 ounces?), so its not a problem. The whole machine will be bolted down anyways. The reason why I don't move the motor is because the two threaded rods would collide with other parts. The way I have it, thby galaxyman7 - Polar Machines, SCARA, Robot Arms
New threaded rod driven arm - 15 years ago
Hey, I have thought about the gear design, and I have decided it is too much trouble both to make it work and to maintain accuracy. Therefore I have changed the design to something much simpler, a threaded rod driven arm. The way it works is this: There is a pivoting holder for the nut on one parts of the frame There is a pivoting holder for the motor on another part They are connected by threby galaxyman7 - Polar Machines, SCARA, Robot Arms
Re: Robotic arm printer - 15 years ago
Hey, I have thought about the gear design, and I have decided it is too much trouble both to make it work and to maintain accuracy. Therefore I have changed the design to something much simpler, a threaded rod driven arm. The way it works is this: There is a pivoting holder for the nut on one parts of the frame There is a pivoting holder for the motor on another part They are connected by threadeby galaxyman7 - Polar Machines, SCARA, Robot Arms
Re: Robotic arm printer - 15 years ago
on a side note, I found a free open source usb to parallel port converter made for CNC. It uses his own free software, which looks good enough for me.by galaxyman7 - Polar Machines, SCARA, Robot Arms
Re: Robotic arm printer - 15 years ago
Yes, transmissive is probably better. I found this opto interrupt transistor on digikey> It only costs $1. It says that it can go up to .05 mm position detection, which translates to .2 mm at the end of the arm. I think this is good enough for making pretty much anything. The only problem is getting a disk that would work with it. Do you know any sources of encoder disks?by galaxyman7 - Polar Machines, SCARA, Robot Arms
Re: Robotic arm printer - 15 years ago
Good point. I don't think potentiometers will be that accurate. Back to optical encoders- An accuracy of .1 mm can be attained using multiple sensors that are offset from eachother (quadrature encoders), but this would require many pins on the microcontroller. The only other way is to convert this parallel data to serial, giving you binary output to the microcontroller. This method basically diby galaxyman7 - Polar Machines, SCARA, Robot Arms
Re: Robotic arm printer - 15 years ago
Actually the way they do it is by having multiple strips of encoder lines offset from each other, with multiple sensors. This way you do not need 1000 lines per inch. Anyways, I was also thinking that a simple potentiometer could be used for the arm joint motors, since they only rotate about 90 degrees maximum. An RC time circuit or something better could read the resistance and get the angle fby galaxyman7 - Polar Machines, SCARA, Robot Arms
Re: Robotic arm printer - 15 years ago
All done with machining! Just need to get the right bolts and nuts now.. pics attachedby galaxyman7 - Polar Machines, SCARA, Robot Arms
Re: Robotic arm printer - 15 years ago
Actually, because of the weight of the extruder, there should be no backlash since the gears will always be in contact on one side of the tooth. The only axis with backlash is the bottom large gear, which is not always in contact with one side. The way to measure backlash is to have an electrical contact home switch, so that when the arm hits the switch, and then reverses, it will run until theby galaxyman7 - Polar Machines, SCARA, Robot Arms
Re: Robotic arm printer - 15 years ago
The machine is polycarbonate. I am not doing it on the wiki. How do I find the page for it, and how do I edit it? By the way, I do have a mill, and I was looking to put an extruder on it. First I have to get this project done. If we can get the software sorted out for this, then I will probably use the robotic arm as a printer instead. The great thing about the robotic arm is that the only outby galaxyman7 - Polar Machines, SCARA, Robot Arms
Re: Robotic arm printer - 15 years ago
I just put the STL files on thingiverse. Also, I just finished some more of the robotic arm. Pics attached.by galaxyman7 - Polar Machines, SCARA, Robot Arms
Re: Robotic arm printer - 15 years ago
New pics for the robotic arm! I just milled these out from some polycarbonate. It was kind of a pain to hold down the smaller pieces when milling, but overall they came out well. My computer also tried to go into standby during the milling process, which totally screwed it up, but luckily it didn't affect anything. I will mill out the base for it and the cross slats in a couple days.by galaxyman7 - Polar Machines, SCARA, Robot Arms